System and method for treating supraventricular tachyarrhythmias

ABSTRACT

A system and method for treating atrial fibrillation using atrial pacing pulses to convert an atrial fibrillation to non-fibrillation atrial arrhythmia prior to delivering a low energy cardioversion/defibrillation shock. The system and method treats atrial fibrillations by first applying a plurality of pacing pulses to the atria which converts the atrial fibrillation to non-fibrillation atrial arrhythmia. Ventricular intervals are concurrently sensed and analyzed while the plurality of electrical pacing pulses are being applied. Upon detecting a period of stable ventricular intervals, the system then proceeds to deliver a low-energy cardioverting/defibrillating pulse of electrical energy across the atria of the heart.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/464,244, filed Dec. 16, 1999 now U.S. Pat. No. 6,430,449, which is adivision of U.S. patent application Ser. No. 09/044,284, filed Mar. 19,1998 now abandonded, the specifications of which are incorporated hereinby reference.

TECHNICAL FIELD

The present invention relates generally to implantable medical devicesand in particular to implantable electrical pulse generators fortreating supraventricular tachyarrhythmias.

BACKGROUND OF INVENTION

Effective, efficient ventricular pumping action depends on propercardiac function. Proper cardiac function, in turn, relies on thesynchronized contractions of the myocardium at regular intervals. Whenthe normal cardiac rhythm is initiated at the sinoatrial node, the heartis said to be in sinus rhythm. However, when the heart experiencesirregularities in the coordinated contraction of the myocardium, due toelectrophysiologic disturbances caused by a disease process or from anelectrical disturbance, the heart is denoted to be arrhythmic. Theresulting cardiac arrhythmia impairs cardiac efficiency and can be apotential life threatening event.

In the supraventricular region of the heart, electrophysiologicdisturbances are called supraventricular tachyarrhythmias (SVT). SVT cantake several distinguishable forms, including paroxysmal atrialtachycardia, atrial flutter, or atrial fibrillation. SVT areself-sustaining process and may be paroxysmal or chronic.

The mechanisms behind these conditions are not well understood, but,generally, the electrical impulses that normally cause sinus rhythm arethought to progress repeatedly around irregular conduction pathwayswithin the heart. These conditions, if uncontrolled, can become lifethreatening if the aberrant electrical impulses enter theatrioventricular node (AV node) in a sporadic and/or at an acceleratedrate and cause an irregular ventricular rate that degenerates into animmediate life threatening ventricular arrhythmia.

Physicians have typically relied on the use of either pharmacologicalagents and/or electrical techniques to control paroxysmal or chronicSVT. Many acute SVT patients convert to sinus rhythm after receivingtreatment with pharmacological agents. However, antiarrhythmicpharmacological agents can have undesirable adverse effects,particularly if the need for drug therapy is chronic.

Alternatively, physicians have used various electrical techniques totreat SVTs. The SVT most frequently treated in this manner is atrialfibrillation. If the atrial fibrillation is acute, the physician mayattempt an electrical cardioversion. This technique has been effectivein converting atrial fibrillation, but it can be quite a painfulexperience for the patient. Implantable atrial cardioverters have alsobeen suggested as a potential treatment for atrial fibrillation.However, the use of these devices can still subject the patient to avery painful and traumatic experience. Furthermore, the energy thesedevices deliver in attempting to treat atrial fibrillation has thepotential for causing transient shock-induced dysfunction as well aspermanent damage to the tissue near the cardioversion electrodes.

SUMMARY OF THE INVENTION

The present invention, in contrast, treats atrial fibrillation in asafe, effective, and more patient acceptable manner. The system of thepresent invention is unique in that it utilizes pacing level electricalenergy impulses applied at a plurality of distinct locations within thesupraventricular region of the heart to reduce the amount of electricalenergy required to cardiovert or defibrillate the supraventricularregion of the heart.

This lower energy method of treating a heart experiencing an atrialfibrillation reduces the potential for transient shock-induceddysfunction as well as permanent damage to the tissue neardefibrillation coil electrodes. As a result, this method of treating aheart experiencing an atrial fibrillation is less painful and lesstraumatic to the patient as compared to the use of conventionalimplantable atrial cardioverters. Also, reducing the required energycould lead to further reductions in the size of the implanted devicewhile extending battery life.

In one embodiment of the present invention, the system includes animplantable housing to which is releasably attached a first atrialcatheter and a ventricular catheter. The first atrial catheter has afirst atrial electrode and a first defibrillation electrode and ispositioned within the heart with the atrial electrode and the firstdefibrillation electrode in a supraventricular region of the heart. Theventricular catheter has a first ventricular electrode, and ispositioned within the heart with the first ventricular electrode in aright ventricular chamber of the heart.

The implantable housing also contains electronic control circuitry whichis electrically connected to the first atrial electrode, the firstdefibrillation electrode, and the first ventricular electrode. Theelectronic control circuitry receives cardiac signals through the firstatrial electrode and the first ventricular electrode, and delivers, upondetecting an atrial fibrillation, a plurality of pacing pulses toconvert the atrial fibrillation to a non-fibrillation atrial arrhythmiasuch as atrial flutter.

In an additional embodiment, the first atrial catheter further includesat least a second atrial electrode and a second defibrillationelectrode. The first atrial catheter is positioned within thesupraventricular region of the heart with the first atrial electrode,the first defibrillation electrode and the second atrial electrodepositioned within a coronary sinus vein of the heart, and the seconddefibrillation electrode within the right atrium chamber or major veinleading to the heart. In a further embodiment, the elongate body of thefirst atrial catheter has a series of lateral deflections thatmechanically biases the first atrial electrode into physical contactwith the coronary sinus vein of the heart.

The electronic control circuitry is electrically connected to the secondatrial electrode and the second defibrillation electrode. The electroniccontrol circuitry receives cardiac signals through the first and secondatrial electrodes and the first ventricular electrode, and delivers,upon detecting an atrial fibrillation, a plurality of pacing pulses toconvert the atrial fibrillation to a non-fibrillation atrial arrhythmiasuch as atrial flutter.

In an alternative embodiment, the system further includes at least asecond atrial catheter, where the second atrial catheter has the secondatrial electrode and the second defibrillation electrode, and ispositioned within the heart with the second atrial electrode and thesecond defibrillation electrode in a supraventricular region of theheart. The electronic control circuitry is electrically connected to thesecond atrial electrode and the second defibrillation electrode. Theelectronic control circuitry receives cardiac signals through the firstand second atrial electrodes and the first ventricular electrode, anddelivers, upon detecting an atrial fibrillation, a plurality of pacingpulses to convert the atrial fibrillation to a non-fibrillation atrialarrhythmia such as atrial flutter.

Concurrent with the delivery of the plurality of pacing pulses, thesystem also senses and analyzes the ventricular rhythm to determine thestability of the ventricular intervals, where a ventricular interval isthe time between the occurrence of sensed ventricular R-waves. In oneembodiment, ventricular interval stability is determined from thevariability of ventricular intervals sensed while the plurality ofpacing pulses are being delivered. A stable ventricular interval has avariability value below a predetermined stability threshold value, andan unstable ventricular interval has a variability value that is greaterthan or equal to the predetermined stability threshold value.

During the delivery of the plurality of pacing pulses, if the systemdetects a period of stable ventricular intervals, it delivers a firstlevel atrial shock to the heart. In one embodiment, the atrial shock isdelivered between the first defibrillation coil and the implantablehousing of the system, where the first defibrillation coil is locatedwithin the right atrium chamber of the heart or major vein leading tothe right atrium chamber of the heart. In an alternative embodiment, theatrial shock is delivered between the first and second defibrillationcoils, where the first defibrillation coil is located within thecoronary sinus adjacent to the left atrium chamber of the heart and thesecond defibrillation coil is located within the right atrium chamber ofthe heart or a major vein leading to the right atrium chamber.

In an additional embodiment, if the plurality of pacing pulses does notconvert the atrial fibrillation, the system repeats the steps ofdelivering a plurality of pacing pulses to the atria. As the system isrepeating delivery of the plurality of pacing pulses it alsoconcurrently senses and analyzes the stability of the ventricularintervals. Upon detecting stable ventricular intervals during therepeated plurality of pacing pulses, the system then proceeds to deliverthe first level atrial shock to the heart to restore sinus rhythm. As aresult, this method of terminating atrial fibrillation by firstconverting it to atrial flutter or some non-fibrillation atrialarrhythmia using pacing pulses then delivering a low-energy first levelatrial shock to restore sinus rhythm provides for a less painful and aless traumatic experience for the patient.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a schematic view of an atrial cardioverter/defibrillator withone embodiment of a first atrial catheter and a ventricular catheterimplanted in a heart from which segments have been removed to showdetails;

FIG. 2 is a block diagram of an atrial cardioverter/defibrillatoraccording to one embodiment of the present invention;

FIG. 3 is a schematic view of an atrial cardioverter/defibrillator withone embodiment of a first atrial catheter and a ventricular catheterimplanted in a heart from which segments have been removed to showdetails;

FIG. 4 is a block diagram of an atrial cardioverter/defibrillatoraccording to one embodiment of the present invention;

FIG. 5 is a schematic view of one embodiment of a catheter according tothe present invention;

FIG. 6 is a schematic view of an atrial cardioverter/defibrillator withone embodiment of a first and second atrial catheter and a ventricularcatheter implanted in a heart from which segments have been removed toshow details;

FIG. 7 is a flow diagram of an embodiment of the present invention; and

FIG. 8 is a flow diagram of an embodiment of the present invention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice and use the invention, andit is to be understood that other embodiments may be utilized and thatelectrical, logical, and structural changes may be made withoutdeparting from the spirit and scope of the present invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense and the scope of the present invention is defined by theappended claims and their equivalents.

The embodiments of the present invention illustrated herein aredescribed as being included in an implantable heartcardioverter/defibrillator/pacemaker, which may include numerous pacingmodes known in the art. The system and method of the present inventioncould also be implemented in an external cardioverter/monitor system.

Referring now to FIGS. 1 and 2 of the drawings, there is shown a system20 including an atrial cardioverter/defibrillator 22 physically andelectrically coupled to a ventricular catheter 24 and a first atrialcatheter 26. The system 20 is implanted in a human body 30 with portionsof the ventricular catheter 24 and the first atrial catheter 26 insertedinto a heart 32 to detect and analyze electric cardiac signals producedby the heart 32 and to provide electrical energy to the heart 32 undercertain predetermined conditions to treat supraventriculartachyarrhythmias, including atrial fibrillation, of the heart 32.

One embodiment of a schematic of the atrial cardioverter/defibrillator22 electronics is shown in FIG. 2. The atrial cardioverter/defibrillator22 comprises an implantable housing 34 which contains electronic controlcircuitry 100. The electronic control circuitry 100 includes terminals,labeled with reference numbers 102, 104, 106 and 108 for connection toelectrodes attached to the surface of the ventricular catheter 24 andthe first atrial catheter 26.

The ventricular catheter 24 is an endocardial lead adapted to bereleasably attached to the implantable housing 34 of the atrialcardioverter/defibrillator 22. The ventricular catheter 24 has anelongate body with a proximal end 50 and a distal end 52 and is shown ashaving a first ventricular electrode 54 located at, or adjacent, thedistal end 52 of the ventricular catheter 24. In one embodiment, thefirst ventricular electrode 54 is a tip electrode positioned at thedistal end 52 of the ventricular catheter 24. Alternatively, the firstventricular electrode 54 is an annular, or a semi-annular ring electrodepositioned adjacent the distal end 52. The first ventricular electrode54 is electrically connected to terminal 102 and to the electroniccontrol circuitry 100 through an electrically insulated conductorprovided within the elongate body of the ventricular catheter 24.

In an additional embodiment, the ventricular catheter 24 furtherincludes a second ventricular electrode 56. The second ventricularelectrode 56 is an annular, or a semi-annular ring electrodeelectrically connected to terminal 104 and to the electronic controlcircuitry 100 through an electrically insulated conductor providedwithin the elongate body of the ventricular catheter 24. The secondventricular electrode 56 is spaced apart and proximal from the firstventricular electrode 54 such that when the ventricular catheter 24 ispositioned within the heart 32 the first ventricular electrode 54 andthe second ventricular electrode 56 reside within a right ventricle 58of the heart 32, with the first ventricular electrode 54 in an apexlocation within the right ventricle 58.

The first atrial catheter 26 is an endocardial lead adapted to bereleasably attached to the implantable housing 34 of the atrialcardioverter/defibrillator 22. The first atrial catheter 26 has anelongate body with a proximal end 60 and a distal end 62 and is shown ashaving a first atrial electrode 64 located at, or adjacent, the distalend 62. In one embodiment, the first atrial electrode 64 is a tipelectrode positioned at the distal end 62 of the first atrial catheter26. Alternatively, the first atrial electrode 64 is an annular, or asemi-annular ring electrode positioned adjacent the distal end 62. Thefirst atrial electrode 64 is electrically connected to terminal 106 andto the electronic control circuitry 100 through an electricallyinsulated conductor provided within the elongate body of the firstatrial catheter 26.

The first atrial catheter 26 also includes a first defibrillationelectrode 66 which is connected to terminal 108 and to the electroniccontrol circuitry 100 through an electrically insulated conductorprovided within the elongate body of the ventricular catheter 24. In oneembodiment, the first defibrillation electrode 66 is a defibrillationcoil electrode as are known in the art. The first defibrillationelectrode 66 is spaced apart and proximal from the first atrialelectrode 64 such that when the first atrial catheter 26 is positionedwithin the heart 32 the first atrial electrode 64 and the firstdefibrillation electrode 66 are positioned within a supraventricularregion 68 of the heart 32.

In one embodiment of the present system, the first atrial catheter 26 ispositioned within the supraventricular region 68 of the heart 32 withthe first atrial electrode 64 and the first defibrillation electrode 66positioned within the right atrium chamber 70 of the heart 32 or a majorvein leading to the right atrium chamber 70 of the heart 32. In oneembodiment, the first atrial catheter 26 is positioned within the rightatrium chamber 70 with the distal end 62 positioned within the rightatrial appendage such that the first atrial electrode 64 make physicalcontact with the right atrium chamber 70 of the heart 32 and the firstdefibrillation electrode 66 is positioned within the right atrium and/ormajor vein leading to the right atrium chamber 70.

The atrial cardioverter/defibrillator 22 is a programmablemicroprocessor-based system, with a microprocessor 110 and a memory 112,which contains parameters for various pacing and sensing modes.Microprocessor 110 includes means for communicating with an internalcontroller, in the form of a RF receiver/transmitter 114. This includesa wire loop antenna 116, whereby it may receive and transmit signals toand from an external controller 118. In this manner, programmingcommands or instructions are transferred to the microprocessor 110 ofthe atrial cardioverter/defibrillator 22 after implant. In oneembodiment operating data is stored in memory 112 during operation. Thisdata may be transferred to the external controller 118 for medicalanalysis.

In the atrial cardioverter/defibrillator 22 of FIG. 2, the firstventricle electrode 54 and the second ventricular electrode 56 arecoupled to a sense amplifier 120, whose output is shown connected to anR-wave detector 122. These components serve to sense and amplify the QRSwaves of the heart, and apply signals indicative thereof to themicroprocessor 110. Among other things, microprocessor 110 responds tothe R-wave detector 122 by providing pacing signals to a pace outputcircuit 124, as needed according to the programmed pacing mode. Paceoutput circuit 124 provides output pacing signals to terminals 102 and104, which connect to the first ventricular electrode 54 and the secondventricular electrode 56, for ventricular pacing.

The first atrial electrode 64 and the first defibrillation electrode 66are coupled to a sense amplifier 126, whose output is connected to aP-wave detector 128. These components serve to sense and amplify theP-waves of the cardiac cycle from the region of the right atrium chamber70, and apply signals indicative thereof to the microprocessor 110.Among other things, microprocessor 110 responds to the atrial signalsfrom the sense amplifier 126 applied to the P-wave detector 128 byproviding pacing signals to the pace output circuit 124, as neededaccording to the programmed pacing mode. Pace output circuit 124provides output pacing signals to terminals 106 and 108, which connectto the first atrial electrode 64 and the first defibrillation electrode66, for normal atrial pacing and atrial pacing according to the presentinvention.

The microprocessor 110 also responds to the cardiac signals sensedwithin the heart 32 using the catheters 24 and 26 by providing signalsto a low-energy output circuit 130 to provide low-levelcardioversion/defibrillation electrical energy to the heart as neededaccording to the method of the present invention. Power to the atrialcardioverter/defibrillator 22 is supplied by an electrochemical battery132 that is housed within the atrial cardioverter/defibrillator 22.

The electronic control circuitry 100 receives cardiac signals throughthe ventricle electrodes 54 and 56, the first atrial electrode 64 andthe first defibrillation electrode 66, and upon detecting an atrialfibrillation, first delivers a plurality of pacing pulses to the heartto convert the atrial fibrillation to a non-fibrillation atrialarrhythmia, such as atrial flutter or non-fibrillation supraventriculararrhythmia, and then delivers a low-energy atrial shock once theventricular intervals stabilize.

In the embodiment shown in FIG. 1, the ventricular catheter 24 and theelectronic control circuitry 100 are utilized for bipolar sensing of theventricular R-wave intervals and the ventricular rate of the heart 32.Bipolar pacing is delivered between the first and the second ventricularelectrodes 54 and 56. In an alternative embodiment, the ventricularcatheter 24 has only a first ventricular electrode 54. Sensingventricular R-wave intervals and ventricular rate is then accomplishedthrough unipolar sensing between the first ventricular electrode 54 andan exposed electrically conductive portion of the implantable housing 34which has been coupled to the sensing amplifier 120. Similarly, unipolarpacing is applied to the heart 32 between the first ventricularelectrode 54 and the conductive implantable housing 34.

Referring again to FIG. 1, the first atrial catheter 26 and theelectronic control circuitry 100 are utilized for bipolar sensing withinthe supraventricular region 68, where bipolar signals from the rightatrium chamber 70 are sensed between the first atrial electrode 64 andthe first defibrillation electrode 66. Bipolar pacing is deliveredbetween the first atrial electrode 64 and the first defibrillationelectrode 66. In an alternative embodiment, unipolar pacing and sensingare provided from the first atrial catheter 26 between the first atrialelectrode 64 and a conductive implantable housing 34.

The atrial cardioverter/defibrillator 22 further includes the low-energyoutput circuit 130, which operates under the control of themicroprocessor 110. The low-energy output circuit 130 is connected tothe first defibrillation electrode terminal 108, which connects to thefirst defibrillation electrode 66, and the conductive implantablehousing 34. In this manner, defibrillation pulses are delivered betweenthe first defibrillation electrode 66 and the implantable housing 34when called for by the microprocessor 110.

Referring now to FIGS. 3, 4 and 5, there is shown an alternativeembodiment of the system 20 including the atrialcardioverter/defibrillator 22 physically and electrically connected toan alternative embodiment of the first atrial catheter 26. The system 20is implanted in the human body 30 with portions of the ventricularcatheter 24 and the first atrial catheter 26 inserted into the heart 32to detect and analyze electric cardiac signals produced by the heart 32and to proved electrical energy to the heart 32 under certainpredetermined conditions to treat supraventricular tachyarrhythmias,including atrial fibrillation, of the heart 32.

Referring now to FIG. 4 there is shown an additional embodiment of theschematic of the atrial cardioverter/defibrillator 22 electronics. Theatrial cardioverter/defibrillator 22 comprises an implantable housing 34which contains electronic control circuitry 100. The electronic controlcircuitry 100 includes terminals, labeled with reference numbers 102,104, 106, 108, 134 and 136 for connection to electrodes attached to thesurface of the ventricular catheter 24 and the first atrial catheter 26.

The first atrial catheter 26 is an endocardial lead adapted to bereleasably attached to the implantable housing 34 of the atrialcardioverter/defibrillator 22. The first atrial catheter 26 has anelongate body with a proximal end 60 and a distal end 62. In oneembodiment, the first atrial catheter 26 has a connector terminal 140 atthe proximal end 60 for attaching the proximal end 60 of the elongatebody to the implantable housing 34 of the atrialcardioverter/defibrillator 22.

In one embodiment, the first atrial catheter 26 is shown as having afirst atrial electrode 64 located between the proximal end 60 and thedistal end 62 of the elongate body. In one embodiment, the first atrialelectrode 64 is an annular, or a semi-annular ring electrode positionedon the elongate body of the first atrial catheter 26. The first atrialelectrode 64 is electrically connected to terminal 106 and to theelectronic control circuitry 100 through a contact end located at theproximal end 60 which is coupled to an electrically insulated conductor148 extending longitudinally within the elongate body of the firstatrial catheter 26.

In an additional embodiment, the first atrial catheter also includes afirst defibrillation electrode 66 which is connected to terminal 108 andto the electronic control circuitry 100 through a contact end located atthe proximal end 60 which is coupled to an electrically insulatedconductor 150 extending longitudinally within the elongate body of thefirst atrial catheter 26. In one embodiment, the first defibrillationelectrode 66 is a defibrillation coil electrode as are known in the art.The first defibrillation electrode 66 is spaced apart and longitudinallyon the peripheral surface of the elongate body from the first atrialelectrode 64 such that when the first atrial catheter 26 is positionedwithin the heart 32 the first atrial electrode 64 and the firstdefibrillation electrode 66 are positioned within a supraventricularregion 68 of the heart 32.

The first atrial catheter 26 further includes a second atrial electrode152 located on the elongate body of the first atrial catheter 26 and isspaced apart and longitudinally on the peripheral surface of theelongate body of the first atrial catheter 26. In one embodiment, thesecond atrial electrode 152 is spaced distally from the first atrialelectrode 64 and the first defibrillation electrode 66 to position thesecond atrial electrode 152 at, or adjacent, the distal end 62 of theelongate body. In one embodiment, the second atrial electrode 152 is atip electrode positioned at the distal end 62 of the first atrialcatheter 26. Alternatively, the second atrial electrode 152 is anannular, or a semi-annular ring electrode positioned adjacent the distalend 62. The second atrial electrode 152 is electrically connected toterminal 134 and to the electronic control circuitry 100 through acontact end located at the proximal end 60 which is coupled to anelectrically insulated conductor 154 extending longitudinally within theelongate body of the first atrial catheter 26.

The first atrial catheter 26 also further includes a seconddefibrillation electrode 156 which is connected to terminal 136 and tothe electronic control circuitry 100 through a contact end located atthe proximal end 60 which is coupled to an electrically insulatedconductor 158 extending longitudinally within the elongate body of thefirst atrial catheter 26. In one embodiment, the second defibrillationelectrode 156 is a defibrillation coil electrode as are known in theart. The second defibrillation electrode 156 is spaced apart andproximal from the first atrial electrode 64 such that when the firstatrial catheter 26 is positioned within the heart 32 the first andsecond atrial electrodes 64 and 152, and the first and seconddefibrillation electrodes 66 and 156 are positioned within asupraventricular region 68 of the heart 32.

In one embodiment, the first atrial catheter 26 is positioned within thesupraventricular region 68 of the heart 32 with the distal end 62positioned within the coronary sinus vein 160 such that the first atrialelectrode 64 is adjacent to and in physical contact with a portion ofthe left atrium chamber 72 of the heart 32 and the first defibrillationelectrode 66 is positioned within the coronary sinus vein 160. In anadditional embodiment, the second atrial electrode 152 is positionedwithin the coronary sinus vein of the heart 32 and the seconddefibrillation electrode 156 positioned within the right atrium chamber70, or some major vein leading to the right atrium chamber 70 of theheart 32.

The first atrial electrode 64, the second atrial electrode 152, thefirst defibrillation electrode 66 and the second defibrillationelectrode 156 are arranged on the elongate body of the first atriacatheter 26 in any combination or subcombination of electrodes. Forexample, in one embodiment the first defibrillation electrode 66 ispositioned at or proximal to the distal end of the first atrial catheter26. The first atrial electrode 64 is spaced apart and proximal from thefirst defibrillation electrode 66 to position the first atrial electrode64 within the coronary sinus vein 160 or within the great cardiac vein.The second atrial electrode 152 is spaced apart and proximal from thefirst atrial electrode 64 to position the second atrial electrode 152 atthe os of the coronary sinus vein 160. Finally, the seconddefibrillation electrode 156 is spaced apart and proximal to the secondatrial electrode 152 to position the second defibrillation electrode 156in the right atrium chamber 70 or a major vein leading to the rightatrium chamber 70 of the heart 32.

In an additional embodiment, the elongate body of the first atrialcatheter 26 has a series of lateral deflections 162 between the proximalend 60 and distal end 62. The series of lateral deflections 162 arearcuate deflections that occur generally within a common plane along theextension of the longitudinal axis of the distal end 62 of the elongatebody. In an additional embodiment, the series of lateral deflections 162occur in opposite directions generally along the extension of alongitudinal axis of the distal end 62 of the elongate body.

In one embodiment, the series of lateral deflections 162 are created byimparting a mechanical bias into the electrically insulated conductorshoused within the elongate body of the first atrial catheter 26 whichcreate a semi-flexible/semi-rigid portion of the elongate body. In analternative embodiment, the series of lateral deflections 162 arecreated by selecting polymers or altering the polymer structure used inconstructing the elongate body of the catheter. In one embodiment, theseries of lateral deflections 162 are intended to stabilize and securethe first atrial catheter 26 within the coronary sinus vein 160.

FIG. 5 shows one embodiment of a series of lateral deflections 162 wherethe elongate body of the first atrial catheter 26 has a first lateraldeflection 164, a second lateral deflection 166, and a third lateraldeflection 168 imparted into the elongate body of the first atrialcatheter 26 that form a series of arcuate deflections. In FIG. 5, thefirst lateral deflection 164 first curves or bends away from thelongitudinal axis of the first atrial catheter's elongate body. Thefirst lateral deflection 164 upon reaching a first maximum deflectionpoint 170 then begins to curve or bend back toward the long axis of theelongate body.

The second lateral deflection 166 begins as the first lateral deflection164 returns the elongate body back to approximately the longitudinalaxis. The second lateral deflection 166 is in the opposite direction ofthe first lateral deflection 164 in the plane of the series of lateraldeflections 162. Once the second lateral deflection 166 reaches a secondmaximum deflection point 172 it begins to curve or bend back toward thelongitudinal axis of the elongate body.

The third lateral deflection 168 begins as the second lateral deflection166 returns the elongate body back to approximately the longitudinalaxis. The third lateral deflection 168 then continues until it reaches athird maximum deflection point 174 and then begins to bend or curve backtoward the longitudinal axis of the elongate body. The third lateraldeflection 168 upon reaching the longitudinal axis of the elongate bodycurves or bends back to once again generally aligns with thelongitudinal axis of the elongate body of the first atrial catheter 26.

In one embodiment, the first maximum deflection point 170 of the firstlateral deflection 164 is spaced longitudinally from the third maximumdeflection point 174 of the third lateral deflection 168 by distances inthe range of 8 to 10 millimeters. In an additional embodiment, the firstmaximum deflection point 170 and the third maximum deflection point 174of the first and the third lateral deflections are spaced horizontallyfrom the second maximum deflection point 172 of the second lateraldeflection in the range of 8 to 11 millimeters.

In a further embodiment, the first atrial electrode 64 is positioned onone of the series of lateral deflections 162 such that the series oflateral deflection 162 causes the first atrial electrode 64 to bemechanically biased into physical contact with the coronary sinus vein160 of the heart 32. For example, the first atrial electrode 64 ispositioned generally in the location of the second maximum deflectionpoint 172 of the second lateral deflection 166 to allow the first atrialelectrode 64 to contact the inner lumen of the coronary sinus vein 160.

The elongate body of the first atrial catheter 26 is made of extrudedimplantable polyurethane, silicone rubber or any other implantableflexible biocompatable polymer. The electrical leads 148, 150, 154 and158 are made of MP35N alloy, or other commonly used electrical leadmetal. The electrodes 64, 66, 152 and 156 are made of implantable metalsuch as platinum/iridium alloy or other commonly used electrode metal.

The first atrial catheter 26 also has a stylet passageway 176 which, inone embodiment, is created by the electrically insulated conductor 154,which has been coiled to create the stylet passageway 176. The styletpassageway 176 extends longitudinally in the elongate body from an inletend located at the proximal end 60 to the distal end 62. The styletpassageway 176 is adapted to receive a guide stylet for stiffening andshaping the second atrial catheter 26 during insertion of the catheterinto the heart 32. The coil of the stylet passageway 176 has sufficientflexibility to straighten due to the presence of a stylet, then returnto the set shape after removal of the stylet.

Referring again to FIG. 4, the atrial cardioverter/defibrillator 22 is aprogrammable microprocessor-based system, with a microprocessor 110 anda memory 112, which contains parameters for various pacing and sensingmodes. Microprocessor 110 includes means for communicating with aninternal controller, in the form of an RF receiver/transmitter 114. Thisincludes a wire loop antenna 116, whereby it may receive and transmitsignals to and from an external controller 118. In this manner,programming commands or instructions are transferred to themicroprocessor 110 of the atrial cardioverter/defibrillator 22 afterimplant. In one embodiment operating data is stored in memory 112 duringoperation. This data may be transferred to the external controller 118for medical analysis.

In the atrial cardioverter/defibrillator 22 of FIG. 4, the firstventricle electrode 54 and the second ventricular electrode 56 arecoupled to a sense amplifier 120, whose output is shown connected to anR-wave detector 122. These components serve to sense and amplify the QRSwaves of the heart, and apply signals indicative thereof to themicroprocessor 110. Among other things, microprocessor 110 responds tothe R-wave detector 122 by providing pacing signals to a pace outputcircuit 124, as needed according to the programmed pacing mode. Paceoutput circuit 124 provides output pacing signals to terminals 102 and104, which connect to the first ventricular electrode 54 and the secondventricular electrode 56, for ventricular pacing.

The second atrial electrode 152 and the first defibrillation electrode66 are coupled to a sense amplifier 126, whose output is connected to aP-wave detector 128. These components serve to sense and amplify theP-waves of the cardiac cycle from the region of the left atrium chamber72, and apply signals indicative thereof to the microprocessor 110.Among other things, microprocessor 110 responds to the atrial signalsfrom the sense amplifier 126 applied to the P-wave detector 128 byproviding pacing signals to the pace output circuit 124, as neededaccording to the programmed pacing mode. Pace output circuit 124provides output pacing signals to terminals 106 and 108, which connectto the second atrial electrode 152 and the first defibrillationelectrode 66, for normal atrial pacing and atrial pacing according tothe present invention.

The first atrial electrode 64 and the second defibrillation electrode156 are coupled to a sense amplifier 138, whose output is connected tothe P-wave detector 128. These components serve to sense and amplify theP-waves of the cardiac cycle from the region of the right atrium chamber70, and apply signals indicative thereof to the microprocessor 110.Among other things, microprocessor 110 responds to the atrial signalsfrom the sense amplified 138 applied to the P-wave detector 128 byproviding pacing signals to the pace output circuit 124, as neededaccording to the programmed pacing mode. Pace output circuit 124provides output pacing signals to terminals 134 and 136, which connectto the first atrial electrode 64 and the second defibrillation electrode156, for atrial pacing and atrial pacing according to the presentinvention.

The microprocessor 110 also responds to the cardiac signals sensedwithin the heart 32 using the catheters 24 and 26 by providing signalsto a low-energy output circuit 130 to provide low-levelcardioversion/defibrillation electrical energy to the heart as neededaccording to the method of the present invention. Power to the atrialcardioverter/defibrillator 22 is supplied by an electrochemical battery132 that is housed within the atrial cardioverter/defibrillator 22.

The electronic control circuitry 100 receives cardiac signals throughthe ventricle electrodes 54, 56, the first and second atrial electrodes64, 152, and the first and second defibrillation electrodes 66, 156, andupon detecting an atrial fibrillation, first delivers a plurality ofpacing pulses to the heart to convert the atrial fibrillation to anon-fibrillation atrial arrhythmia, such as atrial flutter ornon-fibrillation supraventricular arrhythmia, and then delivers alow-energy atrial shock once the ventricular intervals stabilize.

In the embodiment shown in FIG. 3, the ventricular catheter 24 and theelectronic control circuitry 100 are utilized for bipolar sensing of theventricular R-wave intervals and the ventricular rate of the heart 32.Bipolar pacing is delivered between the first and the second ventricularelectrodes 54 and 56. In an alternative embodiment, the ventricularcatheter 24 has only a first ventricular electrode 54. Sensingventricular R-wave intervals and ventricular rate is then accomplishedthrough unipolar sensing between the first ventricular electrode 54 andan exposed electrically conductive portion of the implantable housing 34which has been coupled to the sensing amplifier 120. Similarly, unipolarpacing is applied to the heart 32 between the first ventricularelectrode 54 and the conductive implantable housing 34.

Referring again to FIG. 3, the first atrial catheter 26 and theelectronic control circuitry 100 are utilized for bipolar sensing in twolocations within the supraventricular region 68, where bipolar signalsfrom the left atrium chamber 72 are sensed between the second atrialelectrode 152 and the first defibrillation electrode 66 and bipolarsignals from the right atrium chamber 70 are sensed between the firstatrial electrode 64 and the second defibrillation electrode 156. For thefirst atrial catheter 26, bipolar pacing is delivered between the secondatrial electrode 152 and the first defibrillation electrode 66, andbetween the first atrial electrode 64 and the second defibrillationelectrode 156. In an alternative embodiment, unipolar pacing and sensingare provided from the first atrial catheter 26 between the second atrialelectrode 152 and a conductive implantable housing 34 and/or the firstatrial electrode 64 and the conductive implantable housing 34.

The atrial cardioverter/defibrillator 22 further includes the low-energyoutput circuit 130, which operates under the control of themicroprocessor 110. The low-energy output circuit 130 is connected tothe first and second defibrillation electrode terminals 108 and 136,which connects to the first and second defibrillation electrodes 66 and156. In this manner, defibrillation pulses are delivered between thefirst defibrillation electrode 66 and the second defibrillationelectrode 156 when called for by the microprocessor 110.

In an alternative embodiment, the implantable housing 34 of the system20 is an additional defibrillation electrode, where the implantablehousing 34 has an exposed electrically conductive surface electricallycoupled to the low-energy output circuit 130, such that defibrillationpulses are being delivered between either defibrillation coil electrodes66 or 156 and the implantable housing 34 of the system 20, or betweenany combination of the first defibrillation electrode 66 and/or seconddefibrillation electrode 156 and the implantable housing 34 of thesystem 20.

Referring now to FIG. 6 of the drawings, there is shown an alternativeembodiment of the system 20 further including a second atrial catheter180. The system 20 is implanted in a human body 30 with portions of theventricular catheter 24 and the first atrial catheter 26 and the secondatrial catheter 180 inserted into a heart 32 to detect and analyzeelectric cardiac signals produced by the heart 32 and to provideelectrical energy to the heart 32 under certain predetermined conditionsto treat supraventricular tachyarrhythmias, including atrialfibrillation, of the heart 32.

A schematic of the atrial cardioverter/defibrillator 22 electronics isshown in FIG. 4. The atrial cardioverter/defibrillator 22 comprises animplantable housing 34 which contains electronic control circuitry 100.The electronic control circuitry 100 includes terminals, labeled withreference numbers 102, 104, 106, 108, 134 and 136 for connection toelectrodes attached to the surface of the ventricular catheter 24, andthe first and second atrial catheters 26 and 180.

The ventricular catheter 24 is an endocardial lead adapted to bereleasably attached to the implantable housing 34 of the system 20. Theventricular catheter 24 has an elongate body with a proximal end 50 anda distal end 52 and is shown as having a first ventricular electrode 54located at, or adjacent, the distal end 52 of the ventricular catheter24. In one embodiment, the first ventricular electrode 54 is a tipelectrode positioned at the distal end 52 of the ventricular catheter24. Alternatively, the first ventricular electrode 54 is an annular, ora semi-annular ring electrode positioned adjacent the distal end 52. Thefirst ventricular electrode 54 is electrically connected to terminal 102and to the electronic control circuitry 100 through an electricallyinsulated conductor provided within the elongate body of the ventricularcatheter 24.

In an additional embodiment, the ventricular catheter 24 furtherincludes a second ventricular electrode 56. The second ventricularelectrode 56 is an annular, or a semi-annular ring electrodeelectrically connected to terminal 104 and to the electronic controlcircuitry 100 through an electrically insulated conductor providedwithin the elongate body of the ventricular catheter 24. The secondventricular electrode 56 is spaced apart and proximal from the firstventricular electrode 54 such that when the ventricular catheter 24 ispositioned within the heart 32 the first ventricular electrode 54 andthe second ventricular electrode 56 reside within a right ventricle 58of the heart 32, with the first ventricular electrode 54 in an apexlocation within the right ventricle 58.

The first atrial catheter 26 is an endocardial lead adapted to bereleasably attached to the implantable housing 34 of the system 20. Thefirst atrial catheter 26 has an elongate body with a proximal end 60 anda distal end 62 and is shown as having a first atrial electrode 64located at, or adjacent, the distal end 62. In one embodiment, the firstatrial electrode 64 is a tip electrode positioned at the distal end 62of the first atrial catheter 26. Alternatively, the first atrialelectrode 64 is an annular, or a semi-annular ring electrode positionedadjacent the distal end 62. The first atrial electrode 64 iselectrically connected to terminal 106 and to the electronic controlcircuitry 100 through an electrically insulated conductor providedwithin the elongate body of the first atrial catheter 26.

The first atrial catheter 26 also includes a first defibrillationelectrode 66 which is connected to terminal 108 and to the electroniccontrol circuitry 100 through an electrically insulated conductorprovided within the elongate body of the ventricular catheter 24. In oneembodiment, the first defibrillation electrode 66 is a defibrillationcoil electrode as are known in the art. The first defibrillationelectrode 66 is spaced apart and proximal from the first atrialelectrode 64 such that when the first atrial catheter 26 is positionedwithin the heart 32 the first atrial electrode 64 and the firstdefibrillation electrode 66 are positioned within a supraventricularregion 68 of the heart 32. In one embodiment of the present system, thefirst atrial catheter 26 is positioned within the supraventricularregion 68 of the heart 32 with the distal end 62 positioned within thecoronary sinus vein 160 such that the first atrial electrode 64 isadjacent to and in physical contact with a portion of the left atriumchamber 72 of the heart 32 and the first defibrillation electrode 66 ispositioned within the coronary sinus vein 160.

The second atrial catheter 180 is an endocardial lead adapted to bereleasably attached to the implantable housing 34 of the system 20. Thesecond atrial catheter 180 has an elongate body with a proximal end 182and a distal end 184 and has at least a second atrial electrode locatedon the second atrial catheter 180. In one embodiment, FIG. 6 shows thesecond atrial catheter 180 as having a second atrial electrode 186located at, or adjacent, the distal end 184. In one embodiment, thesecond atrial electrode 186 is a tip electrode positioned at the distalend 184 of the second atrial catheter 180. Alternatively, the secondatrial electrode 186 is an annular, or a semi-annular ring electrodepositioned adjacent the distal end 184. The second atrial electrode 186is electrically connected to terminal 134 and to the electronic controlcircuitry 100 through an electrically insulated conductor providedwithin the elongate body of the second atrial catheter 180.

The second atrial catheter 180 also includes a second defibrillationelectrode 188 which is connected to terminal 136 and to the electroniccontrol circuitry 100 through an electrically insulated conductorprovided within the elongate body of the second atrial catheter 180. Inone embodiment, the second defibrillation electrode 188 is adefibrillation coil electrode as are known in the art. The seconddefibrillation electrode 188 is spaced apart and proximal from thesecond atrial electrode 186 such that when the second atrial catheter180 is positioned within the heart 32 the second atrial electrode 186and the second defibrillation electrode 188 are positioned within theright atrium chamber 70 of the heart 32 or a major vein leading to theright atrium chamber 70 of the heart 32. In one embodiment of thepresent system, the second atrial catheter 28 is positioned within theright atrium chamber 70 with the distal end 76 positioned within theright atrial appendage such that the second atrial electrode 186 makephysical contact with the right atrium chamber 70 of the heart 32 andthe second defibrillation electrode 188 is positioned within the rightatrium and/or major vein leading to the right atrium chamber 70.

In the atrial cardioverter/defibrillator 22 of FIG. 4, the firstventricle electrode 54 and the second ventricular electrode 56 arecoupled to a sense amplifier 120, whose output is shown connected to anR-wave detector 122. These components serve to sense and amplify the QRSwaves of the heart, and apply signals indicative thereof to themicroprocessor 110. Among other things, microprocessor 110 responds tothe R-wave detector 122 by providing pacing signals to a pace outputcircuit 124, as needed according to the programmed pacing mode. Paceoutput circuit 124 provides output pacing signals to terminals 102 and104, which connect to the first ventricular electrode 54 and the secondventricular electrode 56, for ventricular pacing.

The first atrial electrode 64 and the first defibrillation electrode 66are coupled to a sense amplifier 126, whose output is connected to aP-wave detector 128. These components serve to sense and amplify theP-waves of the cardiac cycle from the region of the left atrium chamber72, and apply signals indicative thereof to the microprocessor 110.Among other things, microprocessor 110 responds to the atrial signalsfrom the sense amplifier 126 applied to the P-wave detector 128 byproviding pacing signals to the pace output circuit 124, as neededaccording to the programmed pacing mode. Pace output circuit 124provides output pacing signals to terminals 106 and 108, which connectto the first atrial electrode 64 and the first defibrillation electrode66, for normal atrial pacing and atrial pacing according to the presentinvention.

The second atrial electrode 186 and the second defibrillation electrode188 are coupled to a sense amplifier 138, whose output is connected tothe P-wave detector 128. These components serve to sense and amplify theP-waves of the cardiac cycle from the region of the right atrium chamber70, and apply signals indicative thereof to the microprocessor 110.Among other things, microprocessor 110 responds to the atrial signalsfrom the sense amplified 138 applied to the P-wave detector 128 byproviding pacing signals to the pace output circuit 124, as neededaccording to the programmed pacing mode. Pace output circuit 124provides output pacing signals to terminals 134 and 136, which connectto the second atrial electrode 186 and the second defibrillationelectrode 188, for atrial pacing and atrial pacing according to thepresent invention.

The microprocessor 110 also responds to the cardiac signals sensedwithin the heart 32 using the catheters 24, 26 and 180 by providingsignals to a low-energy output circuit 130 to provide low-levelcardioversion/defibrillation electrical energy to the heart as neededaccording to the method of the present invention. Power to the atrialcardioverter/defibrillator 22 is supplied by an electrochemical battery132 that is housed within the atrial cardioverter/defibrillator 22.

The electronic control circuitry 100 receives cardiac signals throughthe ventricle electrodes 54, 56, the first and second atrial electrodes64, 186, and the first and second defibrillation electrodes 66, 188, andupon detecting an atrial fibrillation, first delivers a plurality ofpacing pulses to the heart to convert the atrial fibrillation to anon-fibrillation atrial arrhythmia, such as atrial flutter ornon-fibrillation supraventricular arrhythmia, and then delivers alow-energy atrial shock once the ventricular intervals stabilize.

In the embodiment shown in FIG. 6, the first and second atrial catheters26, 180 and the electronic control circuitry 100 are utilized forbipolar sensing in two locations within the supraventricular region 68,where bipolar signals from the left atrium chamber 72 are sensed betweenthe first atrial electrode 64 and the first defibrillation electrode 66and bipolar signals from the right atrium chamber 70 are sensed betweenthe second atrial electrode 186 and the second defibrillation electrode188. For the first atrial catheter 26, bipolar pacing is deliveredbetween the first atrial electrode 64 and the first defibrillationelectrode 66, and for the second atrial catheter 180 bipolar pacing isdelivered between the second atrial electrode 186 and the seconddefibrillation electrode 188. In an alternative embodiment, unipolarpacing and sensing are provided from the first and/or the second atrialcatheters 26, 180 between the first atrial electrode 64 and a conductiveimplantable housing 34 and/or the second atrial electrode 186 and theconductive implantable housing 34.

The atrial cardioverter/defibrillator 22 further includes the low-energyoutput circuit 130, which operates under the control of themicroprocessor 110. The low-energy output circuit 130 is connected tothe first and second defibrillation electrode terminals 108 and 136,which connects to the first and second defibrillation electrodes 66 and188. In this manner, defibrillation pulses are delivered between thefirst defibrillation electrode 66 and the second defibrillationelectrode 188 when called for by the microprocessor 110.

In an alternative embodiment, the implantable housing 34 of the system20 is an additional defibrillation electrode, where the implantablehousing 34 has an exposed electrically conductive surface electricallycoupled to the low-energy output circuit 130, such that defibrillationpulses are being delivered between either defibrillation coil electrodes66 or 188 and the implantable housing 34 of the system 20, or betweenany combination of the first defibrillation electrode 66 and/or seconddefibrillation electrode 188 and the implantable housing 34 of thesystem 20.

The ventricular catheter 24 and first and second atrial catheters 26 and180 are releasably attached to and are separated from the atrialcardioverter/defibrillator 22 to facilitate inserting the catheters intothe heart 32. The catheters are inserted transvenously through acephalic or subclavian vein to position the distal ends of the catheterswithin the heart 32. The proximal ends of the catheters are thenattached to the atrial cardioverter/defibrillator 22, where the proximalends of the catheters are adapted to seal together with the terminals102, 104, 106, 108, 134 and 136 of the atrial cardioverter/defibrillator22 to thereby engage the individual electrode conductors and electrodeswith the electronic control circuitry 100. The atrialcardioverter/defibrillator 22 of the system 20 is then positionedsubcutaneously within the human body 30.

By way of further example of an embodiment of the system 20 having atleast a second atrial electrode, it is considered to be within the scopeof the present invention to have additional atrial pacing electrodesadded to the system 20. In one embodiment, a plurality of pacing pulsescan be applied at both a first atrial pacing location and at least twoadditional atrial pacing locations to convert the atrial fibrillation tonon-fibrillation atrial arrhythmia. These additional atrial pacing sitescan be endocardial or epicardial, where in one example the endocardialelectrode can be located in the supraventricular region of the heart andthe epicardial electrode can be located on the left atrial wall of theheart.

FIGS. 7 and 8 illustrates the overall mode of operation of the system 20in treating a heart experiencing an atrial fibrillation. In pacedoperation, the system 20 operates under programmed control to monitorthe ventricular and atrial contractions occurring in the patient'sheart. This is indicated by block 200 in FIG. 7. Monitoring of thecardiac rhythm is accomplished through the sense amps 120, 126 and 138,R-wave detector 122, and P-wave detector 128 which are all under thecontrol of the microprocessor 110. Pacing may be administered as needed,depending upon the type of pacing functions provided in the atrialcardioverter/defibrillator 22.

Decision block 202 tests whether a supraventricular tachyarrhythmia hasbeen detected. This is done through analysis of electrical cardiacsignals from the heart under control of the microprocessor 110 and itsstored programs. In one embodiment of the present invention, the atrialrate is used to determine the presence of a supraventriculartachyarrhythmia. If such condition is not detected, control branches viapath 204 back to the heart beat monitor block 200, and the processcontinually repeats.

If, however, a supraventricular tachyarrhythmia condition is detected atdecision block 202, control passes via path 206 to decision block 208,which tests for the occurrence of atrial fibrillation. In oneembodiment, atrial fibrillation is indicated when the atrial rate isgreater than 250 beats per minute. Alternatively, atrial fibrillation isdetermined thought the analysis of detected cardiac electrogram signals,such as P-wave structure and/or P-wave intervals detected at the firstatrial electrode 64 location and the second atrial electrode 152location. If atrial fibrillation is not detected, control branches toblock 210 for atrial tachyarrhythmia therapies.

If at block 208, an atrial fibrillation is detected, control branches tothe atrial fibrillation therapies of FIG. 8, which first converts theatrial fibrillation to an atrial arrhythmia having a slower and moredistinct cardiac rate and electrogram morphology. This newly creatednon-fibrillation atrial arrhythmia is more amenable tocardioversion/defibrillation, resulting in an increased probability ofsuccessfully converting the atria arrhythmia. Also, thecardioversion/defibrillation energy requirements are less than thoserequired to cardiovert/defibrillate atrial fibrillation. This leads to amore patient acceptable manner of atrial fibrillation conversion.

As a way of determining when an atrial fibrillation has been convertedto a non-fibrillation atrial arrhythmia, such as atrial flutter, by theplurality of pacing pulses, the system 20 monitors the intervals ofventricular contractions. In atrial fibrillation, the ventricularintervals are often rapid and unstable. It is theorized that this is theresult of multiple wavelets, which make up the atrial fibrillation,impinging upon the AV-node. With such intense stimulation of theAV-node, the ventricular interval rate increases, and the stability ofthe intervals decreases due to the random and rapid nature of the atrialfibrillation wavelets.

Atrial fibrillation also requires a large amount of atrial tissue tosustain itself. In contrast, atrial flutter has far fewer wavelets thanatrial fibrillation. By regionally capturing atrial tissue at one ormore locations using pacing pulses of electrical energy, an atrialfibrillation may be converted to atrial flutter. This is because thenumber of wavelets to support the arrhythmia is proportional to theamount of atrial tissue available to support them. So as the amount ofatrial tissue that is being controlled by the pacing pulses increases,less “uncontrolled” atrial tissue is available to sustain fibrillation,until finally the fibrillation is converted to some non-fibrillationatrial arrhythmia.

An indicator that the pacing pulses have converted an atrialfibrillation to atrial flutter, or another non-fibrillation atrialarrhythmia, is that the ventricular intervals are more likely to bestable. A stable ventricular interval is indicated when the standarddeviation of ventricular intervals sensed during the delivery of theplurality of pacing pulses is less than a predetermined stabilitythreshold value. Unstable ventricular intervals have deviation valuesthat are equal to, or exceed, the predetermined stability thresholdvalue.

Ventricular interval stability stems in part from the fact that atrialflutter usually occurs with an AV block, in which the block can have acontraction ratio of, for example, 2:1 or 3:1. Other ratios, however,exist which do not depart from the scope of the present invention. Thisdistinction between ventricular instability during atrial fibrillationand ventricular stability during atrial flutter is utilized by thepresent invention to indicate when and if an atrial fibrillation hasbeen converted by the plurality of pacing pulses, and to indicate when acardioverting/defibrillating pulse of electrical energy is delivered tothe atria to convert the heart to sinus rhythm. In one embodiment of thepresent invention, non-fibrillation atrial arrhythmia, such as an atrialflutter, is defined as having an atrial rate of between 150-250 beatsper minute.

The beginning of the FIG. 8 flow chart, indicated by the symbol “1”, isreached from the symbol “1” of the FIG. 8 flow chart. Referring now toFIG. 8, there is shown one embodiment of the present system where uponthe occurrence or the detection of an atrial fibrillation condition, thesystem 20 treats the supraventricular region 68 of the heart 32 byapplying a plurality of pacing pulses at a first atrial pacing location.The plurality of pacing pulses is delivered to the atria to convert theatrial fibrillation to a non-fibrillation atrial arrhythmia such as anatrial flutter. In one embodiment, the system 20 applies the pluralityof pacing pulses across the second atrial electrode 152 located at theright atrial appendage. In another embodiment, the plurality of pacingpulses are delivered across the first atrial electrode 64 locatedadjacent to the left atrium chamber 72. Alternatively, the pacing pulsesare delivered at other recognized supraventricular pacing locations,such as the os of the coronary sinus or the high right atrium.

The pacing pulse energy is a programmable value, with energy levelsbeing set in the range of between approximately 10 to 15, 7 to 18, or 5to 20 times the patient's diastolic threshold, where 10 times thepatient's diastolic threshold is a suitable value. The diastolicthreshold is a standard electrophysiological measurement to assess theminimum current or voltage needed to influence (capture) the tissue whenit is in diastole. The pacing rate of the plurality of pacing pulses isalso a programmable value which is set in a range of betweenapproximately 120 to 160, 100 to 180, or 80 to 200 beats per minute. Inan alternative embodiment, the plurality of pacing pulses has a pacinginterval that is about 10 percent less than a patient's intrinsiccardiac interval. The plurality of pacing pulses are further deliveredover a predetermined time of between approximately 30 to 40, 20 to 50,or 10 to 60 seconds.

As the plurality of electrical pacing pulses are being applied to thefirst atrial pacing location, the system 20 proceeds to step 302 andbegins sensing and analyzing the ventricular intervals to determinetheir stability. As previously mentioned, a ventricular interval is thetime between successive ventricular contractions, and is measured usingthe detected R-waves. Ventricular intervals are continuously averagedand a standard deviation calculated during the plurality of pacingpulses. The ventricular interval standard deviation is compared to thepredetermined stability threshold value to determine if the sensedventricular intervals are either stable or unstable. Ventricularintervals are stable if their standard deviation is less than thestability threshold value, and are unstable if their standard deviationis greater than or equal to the stability threshold value. Thepredetermined stability threshold value is within a range of between 25to 35, 15 to 45, or 10 to 50 milliseconds.

During step 302, if the electronic control circuitry 100 of the system20 determines that the heart 32 has entered a period of stableventricular intervals (i.e., the ventricular intervals have becomestable) control passes to step 304 where the system 20 proceeds todeliver a first level atrial shock to the heart. The first level atrialshock is a low-energy cardiovertion/defibrillation shock delivered toatria of the heart. In one embodiment, the low-energycardiovertion/defibrillation shock is delivered between the firstdefibrillation electrode 66 placed in the coronary sinus vein 160 andthe second defibrillation electrode 156 within the right atrium chamber70 or major vein leading to the heart. Additionally,cardioverter/defibrillator 22 could be used as additionalcardioversion/defibrillation electrodes to provide a variety of shockingpatterns across the atria Energy values for the first level atrial shockare programmable between 0.5 to 2, 0.4 to 3, or 0.3 to 5 joules.

In an alternative embodiment, after detecting an atrial fibrillation atblock 208 the system 20 applies the plurality of pacing pulses at both afirst atrial pacing location and a second trial pacing location toconvert the atrial fibrillation to a non-fibrillation atrial arrhythmiasuch as an atrial flutter. In one embodiment, the system 20 applies theplurality of pacing pulses across the first atrial electrode 64 locatedwithin the coronary sinus vein 160 adjacent to the left atrium chamber72 and across the second atrial electrode 152 located at the rightatrial appendage. In one embodiment, a predetermined time delay isprovided between the pacing pulses delivered across the second atrialelectrode 152 and the first atrial electrode 64. In this embodiment, apacing pulse is first delivered across the second atrial electrode 152to either a right atrium chamber 70 location or the coronary sinus vein160 location. The pacing pulse delivered across the first atrialelectrode 64 to the left atrium chamber 72 location is then postponedfor the predetermined time delay, where the predetermined time delay isdependant upon the intrinsic intra-atrial conduction delay of thepatient. In one embodiment, the predetermined time delay is aprogrammable time period in the range of between 10 to 100 milliseconds.

At step 302, the system 20 senses the ventricular intervals while theplurality of electrical pacing pulses are being applied to the first andsecond atrial pacing locations, and analyzes the ventricular intervalsto determine ventricular stability, delivering the first level atrialshock to the heart during a period of stable ventricular intervals. If,however, the ventricular intervals do not become stable during theplurality of pacing pulses the method proceeds to step 306. At step 306the system compares the number of attempts that have been made atconverting the atria with a predetermined number of permitted attemptsat converting the atrial fibrillation.

The system 20 is programmed to make two or more attempts, including afinal repeat attempt, at converting an atrial fibrillation. For eachattempt, the system repeats the aforementioned steps of applying aplurality of pacing pulses at one or more atrial pacing locations (e.g.,the first and second atrial pacing electrodes), and sensing andanalyzing the ventricular intervals for stability. If after a finalrepeat attempt a period of stable ventricular intervals is notdetermined during the analyzing step, the system proceeds to step 308and delivers an atrial defibrillation shock to the heart.

The atrial defibrillation shock is a higher energy level shock than thelow-energy level cardioversion shock and is intended to convert atrialfibrillation to sinus rhythm. For stable ventricular intervals thelow-energy level cardioversion shock is delivered in the programmablerange of between 0.1 to 1 Joule. If, however, the atrial defibrillationshock is delivered, it is delivered in the programmable range of between1 to 6 Joules.

Referring back to step 306, in an alternative embodiment, if theplurality of pacing pulses at the first atrial pacing location has notresulted in ventricular stability and the system is not on a finalrepeat attempt, the system 20 returns to step 300 via path 310 andproceeds to repeat steps 300 and 302 by applying a plurality of pacingpulses at a second atrial pacing location to convert atrial fibrillationto a non-fibrillation atrial arrhythmia such as an atrial flutter. Thesecond atrial location is a different pacing location than the firstatrial location. So, in one embodiment, if the plurality of pacingpulses was delivered across the second atrial electrode 146, thesubsequent delivery of a plurality of pacing pulses would be across thefirst atrial pacing electrode 64.

As the plurality of pacing pulses are being delivered across the secondatrial electrode 152, the system 20 senses and analyzes ventricularintervals at step 302. Upon detecting a period of stable ventricularintervals, the system delivers a first level atrial shock to the heartduring a period of stable ventricular intervals. If, however, theplurality of pacing pulses delivered across the second atrial electrode152 fail to convert the atrial fibrillation to non-fibrillation atrialarrhythmia such as atrial flutter, the system 20 returns to step 300 viapathway 310 and proceeds to apply a plurality of pacing pulses at leastonce at both the first atrial pacing location and the second atrialpacing location to convert the atrial fibrillation to a non-fibrillationatrial arrhythmia such as atrial flutter. The system 20 at step 302senses and analyzes ventricular intervals while the plurality ofelectrical pacing pulses are being applied to the first and the secondatrial pacing locations to determine the stability of the ventricularintervals. Upon detecting a period of stable ventricular intervals, thesystem 20 delivers the first level atrial shock to the heart. If,however, the plurality of pacing pulses does not convert the atrialfibrillation to a non-fibrillation fibrillation atrial arrhythmia, suchas atrial flutter, during the final repeat attempt, the system 20delivers an atrial defibrillation shock to the heart at step 308.

Alternatively, after unsuccessfully applying a plurality of pacingpulses at a first atrial pacing location, the system applies a pluralityof pacing pulses at both the first atrial pacing location and a secondatrial pacing location to convert the atrial fibrillation to anon-fibrillation atrial arrhythmia such as an atrial flutter. During theplurality of pacing pulses at both the first and second atrial pacinglocations, the system senses and analyzes the ventricular intervals todetermine the stability of the ventricular intervals. The system 20delivers a first level atrial shock to the heart during a period ofstable ventricular intervals.

If the attempt at converting the atria with the plurality of pacingpulses at both the first and second atrial pacing locations isunsuccessful, the system 20 repeats the step of applying a plurality ofpacing pulses at the first and second atrial pacing locations until thefinal repeat attempt is complete, at which time if the system 20 isunable to convert the atrial fibrillation to a non-fibrillation atrialarrhythmia, such as an atrial flutter, the system 20 proceeds to deliveran atrial defibrillation shock to the heart at step 308.

What is claimed is:
 1. A method for treating a heart, comprising:detecting an atrial fibrillation of the heart; delivering a plurality ofpacing pulses to the heart; determining whether the atrial fibrillationhas been converted to non-fibrillation atrial arrhythmia; and deliveringa low-energy shock to the heart if the atrial fibrillation has beenconverted to non-fibrillation atrial arrhythmia, the energy of thelow-energy shock capable of restoring the heart to a sinus rhythm duringthe non-fibrillation atrial arrhythmia.
 2. The method of claim 1,wherein detecting atrial fibrillation comprises: monitoring atrialcontractions; determining an atrial rate; comparing the atrial rate to apredetermined rate threshold; and indicating that the atrialfibrillation has been detected when the atrial rate exceeds thepredetermined rate threshold.
 3. The method of claim 1, furthercomprising: delivering at least one further plurality of pacing pulsesto the heart if the atrial fibrillation has not been converted tonon-fibrillation atrial arrhythmia; determining whether the atrialfibrillation has been converted to non-fibrillation atrial arrhythmiaafter delivering the at least one further plurality of pacing pulses;delivering the low-energy shock to the heart if the atrial fibrillationhas been converted to non-fibrillation atrial arrhythmia; and deliveringan atrial defibrillation shock to the heart if the atrial fibrillationhas not been converted to non-fibrillation atrial arrhythmia afterdelivering the at least one further plurality of pacing pulses.
 4. Themethod of claim 3, wherein delivering the plurality of pacing pulses tothe heart comprises delivering the plurality of pacing pulses to atleast one of a first and second atrial pacing locations, and deliveringthe at least one further plurality of pacing pulses to the heartcomprises delivering the at least one further plurality of pacing pulsesto at least one of the first and second atrial pacing locations.
 5. Themethod of claim 3, wherein delivering the low-energy shock to the heartcomprises delivering the low-energy shock to at least one of a first anda second atrial defibrillation locations, and delivering the atrialdefibrillation shock to the heart comprises delivering the low-energyshock to at least one of the first and second atrial defibrillationlocations.
 6. The method of claim 1, wherein delivering the plurality ofpacing pulses comprises delivering the plurality of pacing pulses eachhaving a voltage level substantially higher than a diastolic threshold,the diastolic threshold being the minimum voltage level needed tocapture the heart when it is in diastole.
 7. The method of claim 6,wherein the voltage level of the pacing pulses is at least about 5 timesthe diastolic threshold.
 8. The method of claim 6, wherein the voltagelevel of the pacing pulses is less than about 20 times the diastolicthreshold.
 9. The method of claim 6, wherein delivering the plurality ofpacing pulses includes delivering the plurality of pacing pulsesseparated by a pacing interval that is less than a predeterminedpercentage of a measured intrinsic cardiac interval of the heart. 10.The method of claim 6, wherein delivering the plurality of pacing pulsesincludes delivering the plurality of pacing pulses at a programmedpacing rate of at least about 80 beats per minute.
 11. The method ofclaim 6, wherein delivering the plurality of pacing pulses includesdelivering the plurality of pacing pulses at a programmed pacing ratethat is less than about 200 beats per minute.
 12. The method of claim 6,wherein delivering the plurality of pacing pulses includes deliveringthe plurality of pacing pulses over a predetermined period of time. 13.The method of claim 12, wherein the predetermined period of time is atleast about 10 seconds.
 14. The method of claim 12, wherein thepredetermined period of time is less than about 60 seconds.
 15. Themethod of claim 1, wherein determining whether the atrial fibrillationhas been converted to non-fibrillation atrial arrhythmia comprises:monitoring ventricular contractions during the delivery of the pluralityof pacing pulses; measuring ventricular intervals, wherein each of theventricular intervals is a time interval between two successiveventricular contractions; monitoring a stability of the ventricularintervals during the delivery of the plurality of pacing pulses; andindicating that the atrial fibrillation has been converted tonon-fibrillation atrial arrhythmia if the ventricular intervals arestable.
 16. The method of claim 15, wherein monitoring the stability ofthe ventricular intervals comprises: calculating a standard deviation ofthe ventricular intervals; comparing the standard deviation to apredetermined stability threshold; and indicating that the ventricularintervals are stable if the standard deviation is smaller than thepredetermined stability threshold.
 17. The method of claim 1, whereinthe non-fibrillation atrial arrhythmia is an atrial flutter.
 18. Themethod of claim 17, wherein delivering the low-energy shock includesdelivering the low-energy shock having a programmable energy level thatis at least about 0.1 joule.
 19. The method of claim 17, whereindelivering the low-energy shock includes delivering the low-energy shockhaving a programmable energy level that is less than about 1 joule. 20.The method of claim 19, further comprising: delivering at least onefurther plurality of pacing pulses to at least one of a first and secondatrial pacing locations if the atrial fibrillation has not beenconverted to the atrial flutter; determining whether the atrialfibrillation has been converted to the atrial flutter after deliveringthe at least one further plurality of pacing pulses; delivering thelow-energy shock to at least one of a first and second atrialdefibrillation locations if the atrial fibrillation has been convertedto the atrial flutter; and delivering an atrial defibrillation shock tothe at least one of the first and the second atrial defibrillationlocations if the atrial fibrillation has not been converted to theatrial flutter after delivering the at least one further plurality ofpacing pulses.
 21. The method of claim 20, wherein delivering the atrialdefibrillation shock comprises delivering the atrial defibrillationshock having a programmable energy level of at least about 1 joule. 22.The method of claim 20, wherein delivering the atrial defibrillationshock comprises delivering the atrial defibrillation shock having aprogrammable energy level that is less than about 6 joules.
 23. Asystem, comprising; a first atrial electrode adapted to sense a firstatrial signal relating to a beating heart and deliver pacing pulses to afirst atrial pacing location; a first ventricular electrode adapted tosense a first ventricular signal; a first defibrillation electrodeadapted to deliver a first-type shock and a second-type shock to a firstatrial defibrillation location, the first-type shock capable ofrestoring a sinus rhythm during non-fibrillation atrial arrhythmia, thesecond-type shock capable of restoring the sinus rhythm during atrialfibrillation; and control circuitry, coupled to the first atrialelectrode, the first ventricular electrode, and the first defibrillationelectrode, the control circuitry adapted to: detect an atrialfibrillation from the first atrial signal; deliver at least oneplurality of pacing pulses to the first atrial electrode at the firstatrial pacing location; and determine whether the atrial fibrillationhas been converted to non-fibrillation atrial arrhythmia afterdelivering the at least one plurality of pacing pulses; deliver thefirst-type shock to the first atrial defibrillation location if theatrial fibrillation has been converted to non-fibrillation atrialarrhythmia; and deliver the second-type shock to the first atrialdefibrillation location if the atrial fibrillation has not beenconverted to non-fibrillation atrial arrhythmia after delivering the atleast one plurality of pacing pulses.
 24. The system of claim 23,further comprising a second atrial electrode adapted to deliver thefirst plurality of pacing pulses to a second atrial pacing location. 25.The system of claim 23, further comprising a second defibrillationelectrode adapted to deliver the first-type shock and the second-typeshock to a second atrial defibrillation location.
 26. The system ofclaim 23, wherein the control circuitry is adapted to: determine anatrial rate from the first atrial signal; compare the atrial rate to apredetermined threshold rate; and detect the atrial fibrillation whenthe atrial rate is greater than the predetermined threshold rate. 27.The system of claim 23, wherein the control circuitry is adapted to:monitor ventricular contractions in the first ventricular signal duringthe delivery of the first plurality of pacing pulses; determineventricular intervals, wherein each of the ventricular intervals is atime interval between two successive ventricular contractions; monitor astability of the ventricular intervals; and indicate that the atrialfibrillation has been converted to non-fibrillation atrial arrhythmia ifthe ventricular intervals are stable.
 28. The system of claim 27,wherein the control circuitry is adapted to: calculate a standarddeviation of the ventricular intervals; compare the standard deviationto a predetermined stability threshold; and indicate that theventricular intervals are stable if the standard deviation is smallerthan the predetermined stability threshold.